1. 1
   A car mechanic tests a new 12 V car battery before fitting it into a vehicle, to make sure it can supply enough electrical energy to start the engine and power the vehicle's electronics.

   (a)

   The battery's e.m.f. is described as the electrical work done by the battery in moving a unit charge around the complete circuit. In which unit is e.m.f. measured?

   [1 mark]

   • AAmperes (A)
   • BCoulombs (C)
   • CVolts (V)
   • DWatts (W)

   (b)

   The mechanic then connects a voltmeter across just the car's headlamp bulb, in parallel, while the engine is running. What quantity is the voltmeter measuring in this case?

   [1 mark]

   • AThe e.m.f. of the battery
   • BThe current flowing through the bulb
   • CThe total charge stored in the battery
   • DThe potential difference across the bulb

   (c)

   Define potential difference (p.d.), and state how it differs from e.m.f. in terms of where each is measured in the circuit.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An engineer at a hydroelectric power station monitors the e.m.f. produced by the station's generator as water flows through the turbines to drive it.

   (a)

   An engineer at a hydroelectric power station describes the generator's e.m.f. as the electrical work done by the generator in moving a unit charge around the complete circuit. Which equation correctly relates e.m.f. (E), work done (W) and charge (Q)?

   [1 mark]

   • A$E = \frac{Q}{W}$
   • B$E = \frac{W}{Q}$
   • C$E = WQ$
   • D$E = W + Q$

   (b)

   The engineer also measures the p.d. across a large resistive load bank connected to the generator's output. Which equation correctly relates p.d. (V), work done (W) and charge (Q) as it passes through the load?

   [1 mark]

   • A$V = \frac{W}{Q}$
   • B$V = \frac{Q}{W}$
   • C$V = W - Q$
   • D$V = \frac{1}{WQ}$

   (c)

   State the instrument the engineer would use to measure the p.d. across the load bank, and explain how it must be connected in the circuit.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student sets up a simple circuit with a single cell and a lamp to investigate how much electrical work is done as charge passes through the lamp.

   (a)

   A student connects a lamp to a cell and finds that when a charge of 15 C passes through the lamp, 45 J of work is done. Calculate the potential difference across the lamp.

   [3 marks]

   (b)

   The student's cell has an e.m.f. of 3.0 V. Explain what this value of 3.0 V means in terms of the work done on the charge as it passes through the cell, and explain why, for this simple circuit with only the cell and lamp, the p.d. across the lamp is approximately equal to the e.m.f. of the cell.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   In 1800, Alessandro Volta built the first chemical battery, known as the voltaic pile, by stacking discs of two different metals separated by cloth soaked in salt solution, creating a continuous source of electrical energy for the first time.

   (a)

   Explain, using the ideas of e.m.f. and potential difference, what the voltaic pile achieves in a circuit, how e.m.f. is defined and measured, and how the concept of e.m.f. differs from the p.d. that would be measured across a single component connected to the pile.

   [6 marks]

   (b)

   A modern historian recreates Volta's pile and connects it to two identical lamps in series, then measures the p.d. across each lamp separately, and finally measures the e.m.f. of the pile itself using a voltmeter across its terminals with no other components connected. Explain how the historian's measured e.m.f. of the pile should relate to the sum of the two p.d. readings across the lamps, and explain why the p.d. across each individual lamp only accounts for part of the total electrical work being done by the pile.

   [6 marks]

   Total for question 4: 12 marks

End of questions